"We have to eliminate the threat."
As the group's de facto leader, Rick carries the majority of the survivors' collective moral burden. His approach to the Randall problem is a particularly selfish brand of pragmatism: His priority is keeping Lori, Carl, and his unborn child safe, and freeing Randall constitutes an unnecessary risk to that safety. But it's hard not to be disturbed by the arbitrariness of Rick's decision. It was, after all, not too long ago that Rick was the outsider of the survivors' group, when Glen risked his life to save Rick from a particularly aggressive horde of zombies. This isn't the Rick Grimes of the series' pilot episode, who said "I'm sorry this happened to you" to a zombie before he gave it a mercy killing. It isn't even the Rick who pleaded and reasoned with Hershel Greene for temporary sanctuary earlier in the season. But Rick, unlike some of the others, also takes responsibility for his inhumanity; his approach to Randall's execution—which he, like Shane, supports—recalls the philosophy of Ned Stark in HBO's Game of Thrones: "The man who passes the sentence should swing the sword." Rick isn't just willing to be judge and jury; should the need arise, he'll be the executioner.
"Who says we're civilized anymore?"
If The Walking Dead's scale of morality ranges from the humanism of Dale to amorality of Shane, Andrea's arrow has consistently swung toward to the "Shane" side of the equation. Andrea faced the hopelessness of a post-apocalyptic life more quickly than the other survivors when her sister Amy was the series' first major zombie victim. Dale, who thwarted Andrea's attempt to commit suicide at the end of the first season, has repeatedly and unsuccessfully appealed to her sense of decency (in "Judge, Jury, Executioner," he reminds her—and us—that in her former life Andrea was a civil rights attorney). Andrea's sense of humanity seems to have died along with her sister, though there's always the chance that the events of the final moments of "Judge, Jury, Executioner" will resurrect her sense of moral duty.
"I don't want to know... I've made too many mistakes."
There are few characters on The Walking Dead who have had as full an arc as Hershel Greene, who spent months protecting and sustaining his zombified loved ones before Shane gunned each of them down before his eyes. Hershel has subsequently retreated away from religion and back into alcoholism. But his refusal to weigh in on the episode's moral conundrum speaks to a new level of hopelessness for the character. Hershel, like Carol, is content to let someone else make the hard choices—and to stand silently by while violence is carried out in the name of justice. But refusing to intervene one way or the other is a choice in its own right—it's just a more cowardly one.